This project utilizes morphometric techniques as applied to electron micrographs of thin sections, as well as optical diffraction and statistical analysis as applied to electron micrographs of freeze fractured membranes to study: (a) the structure and function of caveolae in rabbit ventricular plasmalemma; (b) the definition of plasma membrane and gap junctional particle distributions in chick embryo hearts examined by freeze fracture; and (c) the structural changes in gap junctions of ventricular myocardial cells and Purkinje fibers under conditions in which the permeability of the gap junctions changes.